1. Field of the Invention
The present invention relates to a stencil printing machine which transfers ink, transuding out of pores in a stencil paper, onto a print medium by transferring the print medium while pressing the print medium against a printing drum on which the stencil paper is mounted.
2. Description of the Related At
As conventional stencil printing machines, there have been an inner press type (disclosed in Japanese Patent Application Laid-open No. 7-132675) and an outer press type (disclosed in Japanese Patent Application Laid-open No. 2001-246828).
The inner press type will be described briefly as follows. As shown in FIG. 1, a stencil printing machine employing the inner press type is provided with a printing drum 110 and a back press roller 101. The printing drum 100 and the back press roller 101 are arranged in a way that the printing drum and the back press roller are each capable of being rotated, and in a state that parts of the outer peripheral surfaces of the printing drum and the back press roller are made closely adjacent to each other. The outer peripheral surface of the printing drum 100 is provided with a stencil clamping unit 100a which clamps an edge of a stencil paper 104. In addition, the outer peripheral wall, except for the stencil clamping unit 100a, is flexible and is constructed of an ink permeable screen 102.
The interior of the printing drum 100 is provided with an ink supplying mechanism 105. As shown in FIG. 2, this ink supplying mechanism 105 includes an inner press roller 106 which is an ink supplying roller, and this inner press roller 106 is attached to a roller supporting member 107 in a way that the inner press roller is capable of being rotated. The inner press roller 106 is configured to be capable of providing displacement between a pressing position in which the roller supporting member 107 is being pressed against the inner peripheral surface of the screen 102 by being pushed in a direction indicated with an arrow a in FIG. 2 and a resting position in which the roller supporting member 107 is being separated away from the inner peripheral surface of the screen 102 by being caused to rotate in a direction indicated with an arrow b in FIG. 2. The inner press roller 106 is cause to provide displacement to the pressing position while a print sheet 111 is passing through, and is caused to provide displacement to the resting position while in other conditions. Additionally, the inner press roller has a function of applying printing pressure from the side of the inner peripheral surface of the screen 102.
In addition, the roller supporting member 107 is supported by a supporting stem 108 in a way that the roller supporting member 107 is capable of being pivoted on the supporting stem 108, and is provided with a doctor roller 109 and an operating rod 110. The doctor roller 109 is shaped like a cylinder, and is fixed to the roller supporting member 107 in a position which is proximate to the inner press roller 106. The operating rod 110 is supported by the roller supporting member 107 in a way that the operating rod 110 is capable of being rotated. The operating rod 110 is arranged in an upper space defined with the outer peripheral walls, of the inner press roller 106 and the doctor roller 109, which are proximate to each other. This upper space is supplied with ink 103 from an ink supplying unit which is not illustrated here.
Next, a printing operation will be described briefly in order. A stencil paper 104 in which a perforated image is formed is mounted on the outer peripheral surface of the screen 102. Then, while in a printing mode, the printing drum 100 and the back press roller 101 are caused to rotate in a direction indicated with an arrow in FIG. 1 while being synchronized with each other, and a print sheet 111 is fed between the printing drum 100 and the back press roller 101.
When the print sheet 111 is fed, the inner press roller 106 presses the screen 102, and is caused to rotate in accordance with the printing drum 100 while pressing in such a way. Ink 103 which has come through the gap between the inner press roller 106 and the doctor roller 109 is put on the outer peripheral surface of the inner press roller 106, and the ink 103 put on the surface is supplied into the inner surface of the screen 102 sequentially by the rotation of the inner press roller 106.
Furthermore, when the inner press roller 106 presses the screen 102, this pressure has the screen 102 expand outwards, and thus the screen 102 is caused to be pressed against the back press roller 101. Then, a print sheet 111 which has been transferred between the printing drum 100 and the back press roller 101 is further transferred between the inner press roller 106 and the back press roller 101 while being pressed by the screen 102 and the stencil paper 104. By this pressure, the ink 103 on the screen 102 is transferred, out of pores in the stencil paper 104, onto the print sheet 111. Thus, an inked image is printed onto the print sheet 111.
Thence, the outer press type will be described briefly as follows. As shown in FIG. 3, a stencil printing machine employing the outer press type includes a printing drum 120. The outer peripheral surface of the printing drum 120 is provided with a stencil clamping unit 120a which clamps an edge of a stencil paper 104. In addition, the outer peripheral wall 120b, except for the stencil clamping unit 120a, is constructed of a porous, ink penetrable member (ink permeable member).
The interior of the printing drum 120 is provided with an ink supplying mechanism 125. This ink supplying mechanism 125 includes: a squeegee roller 126 which is supported so as to be capable of being rotated; and a doctor roller 127 which is arranged in a way that the doctor roller 127 is proximate to the squeegee roller 126. Ink 128 is pooled in an outer space which is surrounded by the squeegee roller 126 and the doctor roller 127. Ink 128 which is put on the outer periphery of the rotating squeegee roller 126 comes through the interval between the squeegee roller 126 and the doctor roller 127, when thus only a prescribed thickness of ink 128 is put on the squeegee roller 126. Then, this prescribed thickness of ink 128 is supplied into the inside of the outer peripheral wall 120b of the printing drum 120.
A pressure roller 130 is arranged in a position which is opposite to the squeegee roller 126, and which is outside the printing drum 120. The pressure roller 130 is configured to be capable of providing displacement between a pressing position in which the pressure roller 130 is being pressed against the outer peripheral wall 120b of the printing drum 120 and a resting position in which the pressure roller 130 is being separated away from the outer peripheral wall 120b of the printing drum 120. The squeegee roller 126 is fixed to a supporting unit which supports the outer peripheral wall 120b of the printing drum 120 in a way that the outer peripheral wall 120b of the printing drum 120 is capable of being rotated. While in a state that the outer peripheral wall 120b of the printing drum 120 is not pressed by the pressure roller 130, the outer peripheral surface of the squeegee roller 126 and the inner peripheral surface of the outer peripheral wall 120b of the printing drum 120 are being slightly separated away. When the outer peripheral wall 120b of the printing drum 120 is pressed by the pressure roller 130, the outer peripheral wall 120b of the printing drum 120 is caused to bend so that the outer peripheral surface of the squeegee roller 126 and the inner peripheral surface of the outer peripheral wall 120b of the printing drum 120 are brought into contact with each other.
Next, a printing operation will be described briefly in order. A stencil paper 104 in which a perforated image is formed is mounted on the our peripheral surface of the outer peripheral wall 120b of the printing drum. While in a printing mode, the outer peripheral wall 120b of the printing drum 120 is caused to rotate in a direction indicated with an arrow in FIG. 3. Hereby, a print sheet 111 is fed between the printing drum 120 and the pressure roller 130.
When the print sheet 111 is fed, the pressure roller 130 presses the outer peripheral wall 120b of the printing drum 120, and hereby the outer peripheral wall 120b is caused to provide displacement inwards. This displacement causes the outer peripheral wall 120b to be pressed against the squeegee roller 126, and hereby the squeegee roller 126 is caused to rotate in accordance with the printing drum 120. Ink 128 which has come through the gap between the squeegee roller 126 and the doctor roller 127 is put on the outer peripheral surface of the squeegee roller 126, and the ink 128 put on the surface is supplied into the inner surface of the outer peripheral wall 120b sequentially by the rotation of the squeegee roller 126.
Furthermore, when the pressure roller 130 presses the outer peripheral wall 120b of the printing drum 120, a print sheet 111 which has been transferred between the printing drum 120 and the pressure roller 130 is further transferred between the squeegee roller 126 and the pressure roller 130 while being pressed by the stencil paper 104. By this pressure, ink 128 on the outer peripheral wall 120b is transferred, out of pores in the stencil paper 104, onto the print sheet 111. Thus, an inked image is printed onto the print sheet 111.
With regard to the stencil printing machines employing the above described, conventional inner and outer press types, however, ink pools are constructed in an outer peripheral space between the inner press roller 106 and the doctor roller 109, and in an outer peripheral space between the squeegee roller 126 and the doctor roller 127. Ink 103 and ink 128 in the ink pools are supplied respectively to the screen 102 of the printing drums 100 and to the outer peripheral wall 120b of the printing drum 120, while a printing operation is performed. As a consequence, in a case that the printing is not performed for a long time, ink 103 and ink 128 held in the respective ink pools as well as ink 103 and 128 put on the printing drums 100 and 120 are left exposed to the atmosphere for a long time. Accordingly, this causes a problem of letting ink change in quality.
In addition, various rollers and the like for supplying ink need to be arranged in the interiors of the printing drums 100 and 120. This causes a problem of making it difficult to miniaturize, and to reduce the weight of, the printing drum 100 and 120.